参数资料
型号: LTC2144CUP-12#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: ADC
英文描述: 2-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQCC64
封装: 9 X 9 MM, LEAD FREE, PLASTIC, MO-220WNJR-5, QFN-64
文件页数: 18/36页
文件大小: 1014K
代理商: LTC2144CUP-12#TRPBF
25
21454312p
LTC2145-12/
LTC2144-12/LTC2143-12
Digital Output Randomizer
Interference from the A/D digital outputs is sometimes
unavoidable. Digital interference may be from capacitive or
inductive coupling or coupling through the ground plane.
Even a tiny coupling factor can cause unwanted tones
in the ADC output spectrum. By randomizing the digital
output before it is transmitted off chip, these unwanted
tones can be randomized which reduces the unwanted
tone amplitude.
The digital output is randomized by applying an exclusive-
OR logic operation between the LSB and all other data
output bits. To decode, the reverse operation is applied;
an exclusive-OR operation is applied between the LSB
and all other bits. The LSB, OF and CLKOUT outputs are
not affected. The output randomizer is enabled by serially
programming mode control register A4.
Alternate Bit Polarity
Another feature that reduces digital feedback on the circuit
board is the alternate bit polarity mode. When this mode
is enabled, all of the odd bits (D1, D3, D5, D7, D9, D11)
are inverted before the output buffers. The even bits (D0,
D2, D4, D6, D8, D10), OF and CLKOUT are not affected.
This can reduce digital currents in the circuit board ground
plane and reduce digital noise, particularly for very small
analog input signals.
When there is a very small signal at the input of the A/D
that is centered around mid-scale, the digital outputs toggle
between mostly 1’s and mostly 0’s. This simultaneous
switching of most of the bits will cause large currents in the
ground plane. By inverting every other bit, the alternate bit
polarity mode makes half of the bits transition high while
half of the bits transition low. This cancels current flow in
the ground plane, reducing the digital noise.
The digital output is decoded at the receiver by inverting
the odd bits (D1, D3, D5, D7, D9, D11). The alternate bit
polarity mode is independent of the digital output random-
izer – either, both or neither function can be on at the same
time. The alternate bit polarity mode is enabled by serially
programming mode control register A4.
APPLICATIONS INFORMATION
CLKOUT
OF
D11/D0
D10/D0
D2/D0
D1/D0
D0
21454312 F15
OF
D11
D10
D2
D1
D0
RANDOMIZER
ON
D11
FPGA
PC BOARD
D10
D2
D1
D0
21454312 F16
D0
D1/D0
D2/D0
D10/D0
D11/D0
OF
CLKOUT
LTC2145-12
Figure 15. Functional Equivalent of Digital Output Randomizer
Figure 16. Unrandomizing a Randomized Digital
Output Signal
相关PDF资料
PDF描述
LTC2144IUP-12#TRPBF 2-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQCC64
LTC2143CUP-12#PBF 2-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQCC64
LTC2145IUP-12#PBF 2-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQCC64
LTC2145CUP-12#TRPBF 2-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQCC64
LTC2144IUP-12#PBF 2-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQCC64
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